ANGLE-RESOLVED PHOTOEMISSION SPECTROSCOPY OF THE 1X1 ORDERED OVERLAYERS ON IODINE-SATURATED GAAS(001) AND INAS(001)

Angle-resolved valence band photoelectron spectra are collected from 1 X 1 ordered overlayers on I-2-saturated GaAs(001)-4 x 1, -c(2 X 8), a nd InAs(001)-c(8 x 2). A high-intensity dispersive surface state, loca ted approximately 4.4 eV below the valence band maximum, is observed i n each case. The state passes through an open lens in the projected bu lk density of states and disperses symmetrically around the surface Br illouin zone edge. For all surfaces studied, the state is stronger whe n excited with the electric field polarized in the [110], as compared to the <(1)over bar 10>], azimuth. Since the state is independent of t he termination of the initial surface, and since iodine bonds primaril y to the outermost element, the state must result from delocalization of the electron states in the overlayer, and is not related to bonding with the substrate.